1. Field of the Invention
The invention relates to treatment of aluminum and aluminum alloy bodies by anodic spark deposition to form a novel lubricant-retaining and mechanically durable surface layer.
2. Description of Related Art
Fuel pump bodies commonly used to supply fuel to internal combustion engines now are made of hard-anodized and water-sealed cast aluminum alloys. For example, an anodized coating thickness of 18 microns, anodized surface roughness of 1.0 micron R.sub.a, and anodized surface hardness of about 250 Hv are specified for certain vehicle cast aluminum alloy fuel pump bodies. Fuel pumps including such hard-anodized and water-sealed pump bodies generally are replaced at least once in the lifetime of most vehicles as a result of the pump body caused by abrasive deposits and fuel impurities. Such abrasive wear occurs as a result of insufficient hardness of the anodized surface layer formed on the cast pump body. In particular, conventional hard anodizing has been found to generally produce a mixture of crystalline and amorphous alumina on the anodized surface with significant amounts of layer porosity even after a water sealing treatment whereby the anodized surface exhibits insufficient hardness and wear resistance.
There thus is a need for a surface treatment for fuel pump bodies made of aluminum and its alloys to impart improved surface hardness and wear resistance thereto.